1. Field
This patent application is directed to the field of ignition coils. It is more specifically directed to measurement of the field that is emitted by ignition coils as a means of analyzing the signals that are delivered to spark plugs by the coils.
2. Description of Related Art
Ignition coils are commonly used to boost a low voltage supply voltage to the very high level that is necessary to ignite and sustain a spark. As is well known, the boosted voltage is usually delivered to a spark plug, typically installed in a combustion engine. The spark ignites fuel, causing increased pressure in the cylinder in which the spark plus is mounted and, in turn, movement of the engine.
In the past, a single ignition coil was used to supply the high voltage needed by several spark plugs. A distributor was connected between the ignition coil and the several spark plugs to sequentially distribute the high voltage that was created by the ignition coil to each of the spark plugs.
A new technology is often used today that is commonly referred to as “coil-on-plug” or “coil-over-plug” (“COP”). Each spark plug is provided with its own ignition coil positioned in close proximity to the spark plug.
As is well known, an analysis of the signal that is delivered to each spark plug can aid in the diagnosis of a problem with a combustion engine or, in the alternative, can confirm that the combustion engine is operating properly. When COP technology is used, however, the coil often blocks access to the spark plug wire. This creates a practical problem in detecting the needed signal.
One approach to overcoming this problem is to place a signal detector in close proximity to the ignition coil. The signal detector detects variations in the field that are caused by the ignition coil, typically by its secondary winding. This is typically accomplished by using a capacitive or inductive component in the signal detector. Examples of such signal detectors are described in U.S. Pat. No. 6,396,277 B1, the content of which is incorporated herein by reference.
A single signal detector is often used to detect the signals on several plugs. The process usually begins by the mechanic clipping the signal detector to the housing of a first ignition coil. The engine is then operated. The ignition coil generates a field each time the plug is fired. This voltage is typically proportional to the voltage that the coil delivers to the plug. The signal detector detects this field. The detected signal may then be processed to extract the most relevant information and the results are reported to the mechanic. The mechanic then typically detaches the detector from the first housing, attaches it to the housing of another ignition coil, and the process repeats, often until the voltages to all of the plugs have been studied.
Unfortunately, a single engine sometimes uses different models of COPs on its various cylinders. In V-6 engines, for example, some manufacturers use one COP model on the front cylinders, but a different COP model on the rear cylinders. These different COP models often generate fields of different intensity, even when they are delivering the same voltage to their respective spark plugs.
In some Nissan cars, for example, a Nissan model 22448-31 U01 COP is installed in the rear cylinders, while a Nissan model 22448-2Y000 COP is installed in the front cylinders. The 31U01, however, typically generates over twice the field strength that the 2Y000 generates when delivering the same output voltage.
This field strength differential often creates confusion during use, particularly with mechanics that are not aware of the differential. This confusion sometimes leads to the erroneous conclusion that a particular COP is not operating properly and, in turn, to unnecessary and unfruitful repairs.
Even when the mechanic is skilled enough not to be confused by the field strength differences, the field strength differential is sometimes greater than the dynamic range of the signal detector. This often requires different signal detectors to be stocked and used to fully test a single engine.